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SI ECO Fix Order: Debug Playbook

Debug Playbook for SI ECO Fix Order.

Debug playbook

Debug Playbook for SI ECO Fix Order focuses on post-ECO SI WNS recovery, reroute count, spacing violations cleared. The goal is to connect the observable symptom to timing mechanism, ownership, and regression risk.

STA debug is a search for the FIRST deviation, not the loudest downstream symptom. Hold failures after setup ECO are a classic example of fixing the wrong layer first.

Root-cause tree

diagram

ROOT-CAUSE TREE — SI ECO Fix Order

post-ECO SI WNS recovery, reroute count, spacing violations cleared looks wrong
        |
   same netlist tag?
     /        \
   no          yes
   |            |
 view/SDC     real path or
 mismatch     constraint bug
 /    \           |
lib   SPEF    delay breakdown
diff  diff    cell vs net

Freeze the failing netlist tag, SDC revision, and SPEF corner.
Find the first constraint or delay anomaly on the critical path.
Map the path to launch/capture clocks and path group.
Classify the failure: constraint bug, view mismatch, cell delay, net delay, or SI.
Prove the mechanism with one reduced path or isolated scenario.
Patch the smallest owner-controlled fix and rerun setup, hold, and MMMC.

Review memo template

diagram

STAFF STA REVIEW MEMO — SI Timing & Noise / SI ECO Fix Order

1. Symptom
   - Watched metric: post-ECO SI WNS recovery, reroute count, spacing violations cleared
   - Failing scenario: <corner/mode/view>
   - Path group: <reg2reg / in2reg / reg2out / async>
   - Database tags: <netlist, SDC, SPEF, lib>

2. Mechanism hypothesis
   - Primary mechanism: SI fixes use spacing, shielding, sizing, and reroute; order matters because a setup fix can worsen hold or noise elsewhere.
   - Competing hypothesis: <constraint bug, view mismatch, cell delay, net delay, SI>
   - Missing evidence: <report_timing, clock report, constraint trace>

3. Proposed action
   - Minimal reversible change: <SDC fix, sizing, VT swap, route, useful skew>
   - Expected metric movement: <WNS/TNS delta>
   - Regression risk: hold, other corners, SI, leakage

4. Signoff
   - Re-run artifact: ECO change list, before/after SI report, regression matrix
   - Required owners: PD owner, SI owner, STA lead
   - Final decision: ECO, waive, constraint fix, or escalate

STA deep dive

Coupling makes delay a function of neighbors, not just wire RC.

Concept diagram

diagram

SI ON VICTIM

victim net delay = base_RC + coupling_from_aggressors

Metric graph

diagram

DELTA DELAY ON CRITICAL PATHS

no SI   ████████  1.2ns
with SI ██████████  1.35ns  (+150ps)

Reports and artifacts

delta delay report
aggressor list
noise peaks
SI WNS delta

Mini case study

Setup fixed by upsize but SI worsened — spacing ECO on bus bits recovered margin.

Debug branches

Re-run SI after every timing ECO
Shield wide switching buses

Senior review question

Ask: what corner/mode/view proves this topic is closed or failing?

Key takeaways

State corner, mode, view, and database tag with every slack claim.
Run setup and hold plus MMMC regression after every ECO.

Common pitfalls

Comparing STA runs with different SPEF or SDC tags.
Broad false_path to green-wash violations.
Setup-only ECO without hold check.

Principal STA review addendum

SI fixes use spacing, shielding, sizing, and reroute; order matters because a setup fix can worsen hold or noise elsewhere.

Metric: post-ECO SI WNS recovery, reroute count, spacing violations cleared

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